Method of producing fuming sulphuric acid having a high concentration



Feb. 23, 1937. c. B. voN GIRSEWALD ET Al. 2,071,598

METHOD OF PRODUCING FUMING SULPHURIC ACID HAVING A HIGH CONCENTRATIONFiled Dec. 24, 1935 Max 5J Q" Patented F eb. 23, 1937 UNITED STATESPATENT OFFICE METHOD OF PRODUCIN G rFUMINGr SUL- PHURIC ACID HAVING AHIGH CONCEN- TRATION Conway Baron von Girsewald, Wolfhart Secke,

and Max Wohlwill,

Frankfort-on-the-Main,

Germany, assignors to American Lurgi Corporation, New York, N. Y., acorporation of New York 15 Claims.

The present invention relates to a method of producing fuming sulphuricacid, and, more particularly, to a'method of producing fuming sulphuricacid having a high S03 concentration.

Heretofore, fuming sulphuric acid has been generally produced byabsorbing S03, obtained from a contact apparatus in concentratedsulphuric aci-d. In the conventional processes, usually pre-dried andcleaned SO2 and gases conv acid containing about 97% H2S04.

taining oxygen were oxidized to S03, by means of suitable contact massesor catalysts. The hot gases leaving the contact masses have been cooledand washed with a great excess of cold sulphuric The excess of sulphuriclacid has been necessary because the absorption of S03 would releaseconsiderable amounts of heat which raised the temperature of thereacting substances. 0n the other hand, such rise in temperature wasextremely detri- -mental to the process of concentrating uming sulphuricacid because, according to Knietsch at a temperature of 45 C. thepressure values of S03 amount to 43.6 mm. oi mercury in a fumingsulphuric acid of 35%. Thus, the art of producing iurning sulphuric acidon an industrial scale was nfronted with a grave problem because toogreat an excess of cold sulphuric acid would cause undue dilution oi theformed fuming sulphuric acid and, on the other hand, if too little coldsulphuric acid has been added the temperature would rise and woulddecrease the concentration in view of the fact that the solubility ofS03 in sulphuric acid is reduced when the temperature of the acid isincreased. For this reason, the fuming sulphuric .acid heretoforeproduced industrially did not have a concentration higher than about 27%S03.

It has been proposed to reduce the quantity of the circulatingacid andto provide external cooling for maintaining the temperature of the acidwithin preferred limits. In a process of this character a tubular coolersprayed with water is employed for producing fuming sulphuric acid oihigh concentration. Concentrations of only about 20% have been obtainedat best, probably due to the fact that the temperatures at the lower endof the condenser tube were too high.

it has been also proposed to produce furning sulphuric acid by means ofdirect condensation of SOM-H20. 0i course,'in this case the amount ofheat produced was even higher due to the fact that the absorption heatof S03 and the hydration and condensation heat oi the simultaneouslyformed HzSOi were added. Cooling of the reaction chambers of this typeof condensation has caused great diiiiculties because any chilling ofthe gases containing S03 and H20 had to be carefully avoided in order toprevent the formation of practically non-condensable acid mists.According to a recent process disclosed in our copending applicationsSerial No. '711,198 and Serial No. 714,562, the latter now being U. S.Patent No. 2,017,676, the formation of mists can be prevented in thecondensation of sulphuric acid by adequately regulating the coolingspeed and by providing aA suitable heat exchange apparatus for carryingout such cooling and condensation process. In our earlier process,however, the con-A densation has been carried out under such conditionsthat steam was present in at least suicient quantity for the formationof I-I2S04.

It is an object of the present invention to pro* vide an improvedprocess of producing fuming sulphuric acid which makes it possible toobtain fuming sulphuric acid of a very high concentration.

It isvanother object of the present invention to provide a process ofproducing ruining sulphuric acid having a concentration of up to 35%S03, which process is simple and economical and which can be readilycarriedout on an industrial scale.

It is a further object of the invention to provide an improved processfor producing fuming sulphuric acid, which yields a fuming sulphuricacid having an S03 concentration unobtainable heretofore and which maybe carried out in conventional `and existing installations Withoutrequiring any substantial changes.

The invention also contemplates a process of producing iuming sulphuricacid by condensing H2504 `from gases containing steam but ininsuiiicient quantity for converting the total S03 present to sulphuricacid.

Other and further objects and advantages of the invention will becomeapparent from the following description taken in conjunction with theaccompanying drawing, in which Fig. 1 illustrates a longitudinalsectional view of an apparatus for carrying the process oi the inventioninto practice;

Fig. 2 is a cross section through the apparatus taken onlinef2-2 of Fig.1; and

Figj3 shows an enlarged longitudinal sectional view of a portion of theapparatus depicted in Fig. 1.

Broadly stated, a process for the production of fuming sulphuric acid isprovided according to the principles of the present invention bycondensing H2S04 from gases which do vnot contain sufcient quantity ofsteam for converting thel total quantity of the S03 present to sulphuricacid. The present process comprises introducing hot gases containing H20and S03 into a condensation apparatus, for example, ofthe type describedin our U. S. Patent No. 2,017,676 and of which a short description willbe given hereinafter. In contrast, however, to conventional processes,the gases are not introduced at the bottom or lower portion of theapparatus, but at the top or upper portion thereof so that the gases andthe formed sulphuric acid will pass co-currently through the apparatusfrom the top to the bottom. The reaction proceeds in the followingmanner:-

In the upper portion of the apparatus, the quantity of sulphuric acidcorresponding to the quantity of H2O present is rst condensed byexternal and indirect cooling. The condensed acid trickles downwards inthe condensing tubes containing a filling material and during itsdownward ow and further cooling absorbs a considerable portion of theexcess S03 and forms furning sulphuric acid of high concentration. It isone of the essential concepts of the invention to have both the gasesand the formed sulphuric acid condensate iiowing co-currently from thetop of the apparatus to the bottom thereof so that the fuming sulphuricacid is withdrawn at relatively low temperatures whereby dilution of thefiuning sulphuric acid caused by the relatively high vapor pressure ofS03 at higher temperatures is prevented. 0n the other hand, the coolingagent is conducted countercurrently to the gases and to the acid formedin the apparatus whereby relatively high temperatures of the coolingagent are maintained in the upper portion of the apparatus wherecarefully controlled cooling is essential, Aand stronger and intenseexternal cooling is provided in the lower portion of the apparatus whereit is important to maintain low nal temperatures within the condensingtubes. Thus, in contrast to the conventional processes, which had towithdraw the fuming sulphuric acid at relatively high temperatures, thefuming sulphuric acid is, according to the principles of the presentinvention, withdrawn at the lower end of the apparatus at relatively lowtemperatiues whereby considerably higher concentrations are obtainablethan by the prior processes employing large quantities of concentratedsulphuric acid for the purpose of absorption and cooling. A furtherimportant advantage of the process of the invention is that the acid owsdownward by gravity and the necessity of pumping the absorption acid iseliminated.

The process embodying the present invention may be carried out indiierent suitable types of apparatus. We prefer, however, to vemploy thetype of apparatus which is disclosed in our U. S. Patent No. 2,017,676and which is described in the following short description taken inconjunction with the accompanying drawing.

The apparatus consists of an outer casing or shell a, preferably ofsheet iron, having inlets and outlets m and n. A plurality of tubes B isdisposed in said shell, each of said tubes being formed by twoconcentric tubes of diierent materials, c and d, preferably spaced apartwith the intermediate space lled with a filling material e. The outertube c, which contacts the cooling liquid, is made of a material of highmechanical strength, for example, metal, such as stainless steel or thelike, while the inner tube d is made oi a ceramic material such asquartz, which need not have great mechanical strength but is capable ofresisting sulphuric acid at high temperatures. The application ofceramic material has the further advantage that it is a poor conductorof heat whereby quick chilling of the reaction gases is prevented. Thespace in between the two tubes is filled with a suitable powderedmaterial as powdered metals or fine sea sand which adds to the stabilityof the structure and permits slight relative displacement of the twotubes under the inuence of heat. The reaction gases are introduced atthe top 1c of the apparatus and the condensed uming sulphuric acid ofhigh concentration is discharged at the bottom of the apparatus througha Siphon seal z'. The cooling medium, water or oil is introduced at thebottom of the apparatus through inlets M and is discharged at the top ofthe apparatus through outlet N. Thus, the incoming gases and vapors aresubjected to carefully controlled and moderate cooling at the top of theapparatus, where the cooling medium is much warmer, while at the bottomof the apparatus the condensed firming sulphurlc acid is cooled withfresh and low temperature cooling agent so that it is capable o1absorbing great amounts of S03.

It is to be observed that although the conducting of gases cocurrcntlythrough the condensing apparatus has already been contemplated in otherarts, it has never been employed in the preparation of turning sulphuricacid of high concentration and in such manner that in the upper ortionof the apparatus the condensation of the sulphuric acid and in the lowerportion thereof the absorption of the excess quantity of S03 is carriedout to produce fuming sulphuric acid of high concentration. For example,even though the cooling would be carefully controlled, the condensationof fuming sulphuric acid carried out countercurrently would produce atbest concentrations oi 20% S03 in the tuning acid such as is produced bythe conventional processes.

In addition to the advantages described hereinabove, the presentinvention appears to be in two directions. First, a uming sulphuric acidof considerably higher concentration may be obtained than was possibleheretofore. In the prior art a concentration of 27% S03 has usually beenconsidered as the upper practical limit while according to the presentprocess, concentrations of 35% are readily obtained. It would bepossible to obtain even higher concentrations but for the presence of amaximum in the melting point curve H2S04-S03, which is about 36 C. for45% S03. In view of the fact, however, that this temperature should notbe exceeded in order to keep the vapor pressure of S03 at a low value,there is a certain danger that at such extreme concentrations theapparatus may be clogged up with turning sulphuric acid crystals whichare frozen out. 0n the other hand, even obtaining a fuming sulphuricacid having a concentration as high as 35% represents great technicalprogress over the uppermost possibilities of prior processes.

The other important advantage of the present process consists in thepossibility of conducting gases containing only small amounts of steamover the contact apparatus. According to the principles of theinvention, it is unimportant whether this steam is passed over thecatalyst or is added after the flow has passed through the contactapparatus. t is possible, for example, to conduct combustion gasescontaining SO2 produced with air which has not been previouslydehumidied but contains its natural moisture,

directly into the contact apparatus without the necessity of previouslydrying the air by means of highly concentrated sulphuric acid. Thus, thecost of producing fuming sulphuric acid is considerably reduced by thepossibility of omitting this step which was necessary in all priorprocesses.

Very naturally, when producing fuming sulphuric acid of the describedhigh concentration, small quantities of S03 will be retained in thegases leaving the apparatus. For this reason, it is advisable to connecta small apparatus to the condensation apparatus, for washing the gaseswith concentrated sulphuric acid. f course, the quantity of S03 inquestion is only a small fraction of the total quantity of S03 which ispresent and its absorption is greatly facilitated by the circumstancethat due to the efficient cooling provided in the apparatus, the gasesarrive to the washer at a relatively low temperature.

For the purpose of giving those skilled in the art a betterunderstanding of the present invention, the following illustrativeexample is given:-

In a plant having a daily gas capacity of about 60,000 cubic meters, thegas is to be treated in accordance with the principles of the invention,the volume of the gas being gured at 0 C. and '760 mm. of mercury. Thegas contains 7% S03 and in addition about 3.3% H2O. The gas has atemperature of about 350 C. when it is introduced at the top of thewater-cooled tubular cooler of the chara-cter described and has atemperature of 26 C. when it leaves the apparatus. The cooling water isintroduced at the bottom of the apparatus and has the temperature of thewater mains or of the water supply and during the time it rises to thetop of the apparatus, the water is heated up to boiling temperature.Thus, in the upper portion of the apparatus, sulphuric acid is condensedcorresponding to the quantity of H20 which is present. During itsdownward flow, this acid takes up so much S03 that at the lower end ofthe apparatus daily about 13.5 metric tons of fuming sulphuric acidhaving 34% free S03 may be withdrawn. The waste gasesvof the coolercontain about 3.4 tons of S03 corresponding to the vapor pressure of 34%fuming sulphuric acid at 26 C. 'Ihis residual quantity of S03 is washedout with sulphuric acid of 95% in an adjoining washing tower. In thewashing process, sulphuric acid of 97% is obtained which is either soldas such, or after being diluted to a concentration of 95% may bereturned to the washing tower.

It is to be observed that the present invention provides a process ofproducing furning sulphuric acid having a high concentration (forexample 35%) by co-currently passing a downward flowing stream of H20vapor and a large excess of S03 vapor in a vertical condensation chamberand by establishing an upward flow of a cooling liquid (for example,water, oil, etc.) around the external surface of said chamber. In orderto prevent the formation of dilicultly condensable mists, the velocityof flow of the vapors is so adjusted as to be between about 0.8 to about5.0 metres per second. It is essential that the time required forcooling the vapors from the dew point thereof to 140 C. should be notless than about 0.2 to about 0.6 second. Temperatures graduallydecreasing from about 140 C. to about 26 C. are maintained in the lowerportion of the condensation chamber to facilitate absorption ofrelatively large quantities of S03 by means of the condensed liquidH2S04. If these conditions are maintained the danger of mist formationis positively eliminated and fuming sulphuric acid having a highconcentration up to 35% may be produced in a simple and economicalmanner.

We claim:

1. The method of producing fuming sulphuric acid which comprisesestablishing a decreasing temperature gradient from the top to thebottom of a condensation chamber, introducing H20 and S03 vapors at theupper portion of said chamber, said S03 being present in substantialexcess over the quantity necessary to form H2SO4 with the H20 present,condensing H2S04 inthe uppermost portion of said chamber correspondingto the quantity of H20 present, conducting the remaining S03 vaporsdownward co-currently with the thus-formed H2504, absorbing substantialquantities of the excess S03 by means of said condensed H2S04 trickling'downwards, and withdrawing fuming sulphuric acid at the bottom of saidchamber.

2. The method of producing fuming sulphuric acid which comprisesestablishing gradually decreasing cooling temperatures in an elongatedcondensation chamber, introducing H20 and S03 vapors into the upperportion of said chamber, said S03 being present in substantial excessover the quantity necessary to form H2SO4 with the H2O present,condensing H2504 at relatively high condensing temperatures in theuppermost portion of said chamber corresponding to the quantity of H20present, conducting the remaining S03 vapors downward co-currently withthe thus-formed H2504, subjecting the downward flowing condensed H2S04and the S03 vapors to progressively colder temperatures, absorbingsubstantial quantities of the excess S03 by means of said condensedH2S04 trickling downwards at relatively low cooling temperatures to formfuming sulphuric acid, and withdrawing relatively cold fuming sulphuricacid containing a high concentration of S03 at the bottom portion ofsaid chamber.

3. The method of producing fuming sulphuric acid which comprisesintroducing H20 and S03 vapors into the top portion of a Verticalcondensation chamber, said S03 being present in substantial excess overthe quantity necessary to form H2S04 with the H20 present, establishingan external upward flow of a cooling medium around the outer surface ofsaid chamber in controlled heat exchange therewith, condensing H2S04 todroplets corresponding to the quantity of H20 present at amist-preventing' cooling rate in the upper portion of said chamber,permitting said droplets of condensed acid to descend by gravity in saidchamber co-currently and in intimate contact with the residual S03vapors to form a film, subjecting said film of condensed H2S04 toprogressively colder temperatures, absorbing relatively large amounts ofS03 by means of said nlm at gradually decreasing cooling temperatures,and withdrawing highly concentrated fuming sulphuric acid at the bottomportion of said chamber at a region where the temperature SC3-absorbingtemperatures in the lower portions thereof, introducing H20 and S03vapors at the top of said chamber, said S03 being present in substantialexcess over the quantity necessary to form H2SC4 with the H20 present,condensing H2S04 in the top portion of said chamber from the H20 andfrom a portion of the S03 present, permitting said I-I2S04 to descend bygravity cocurrentiy and in intimate contact with the residual S03vapors, cooling said condensed H2S04 as it flows downward, absorbingrelatively substantial quantities of S03 by means of said condensedH2504 during its downward flow at gradually decreasing coolingtemperatures, and withdrawing highly concentrated fuming sulphuric acidat the bottom portion of said chamber at a region where the temperatureis approximately the coldest.

5. The method of producing fuming sulphuric acid which comprisesestablishing a downward ow of S03 and H20 vapors in a vertical tubularcondensation chamber, said S03 being present in substantial excess overthe quantity necessary to form H2S04 with the H20 present, establishingan upward flow of cooling liquid around the external surface of saidchamber, in heat exchange with said chamber to maintain amist-preventing rate of cooling and relatively high condensationtemperatures at the upper portion of said chamber and graduallydecreasing S03-absorbing temperatures in the lower portions of saidchamber, condensing H2S04 corresponding approximately to the quantity ofthe H20 present in the upper portion of said chamber, absorbingsubstantial quantities of S03 by means of said condensed H2S04 duringits downward flow while being subjected to decreasing temperatures, andwithdrawing fuming sulphuric acid of high concentration at the bottom ofsaid chamber in a region where the temperature is approximately thelowest.

6. The method of producing fuining sulphuric acid which comprisesintroducing H20 and S03 vapors at a temperature of about 350 C. at thetop of a tubular vertical condensation chamber, said S03 being presentin substantial excess over the quantity necessary to form H2S04 with theH2O present, establishing an external upward flow of a cooling liquid ofthe group consisting of cooling water, oil and the like, around theouter surface of said chamber in controlled heat exchange with thecontents thereof, condensing H2S04 to droplets corresponding to thequantity of H20 present at mist-preventing cooling rate in the upperportion of said chamber, permitting said droplets of H2S04 to descend bygravity in said chamber co-currently and in intimate contact with theresidual S03 vapors to form a liquid film, absorbing relatively largeamounts of S03 vapors by means of said liquid lm at gradually decreasingcooling temperatures, and withdrawing highly concentrated fumingsulphuric acid at the bottom portion of said chamber at a temperature ofabout 26 C.

7. The method of producing fuming sulphuric acid which comprisesestablishing a downward flow of S03 and H20 vapors in a verticalcondensation chamber, said S03 being present in substantial excess overthe quantity necessary to form H2S04 with the H20 present, establishingan upward flow of cooling liquid around the external surface of saidchamber, in greatly retarded heat exchange with the contents of saidchamber to maintain a mist-preventing rate of cooling and relativelyhigh condensing temperatures at the upper portion of said chamber andgradually decreasing temperatures promoting absorption of the S03 in thelower portions of said chamber, condensing liquid H2S04 corresponding tothe quantity of the H20 present in the upper portions of said chamber,absorbing substantial quantities of S03 vapor by means of said condensedliquid H2S04 during its downward flow while being subjected todecreasing temperatures, and withdrawing fuming sulphuric acid of highconcentration at the bottom portion of said chamber where thetemperature is the lowest.

8. The method of producing fuming sulphuric acid which comprisesintroducing H20 and S03 gases at the top of a plurality of verticalcondensation tubes of low heat conductivity, said S03 being present insubstantial excess over the quantity necessary for the formation ofH2S04 with the H2O present, externally cooling said condensation tubeswith a liquid cooling agent flowing in an upward direction, condensingH2S04 corresponding to the quantity of the H20 present in the upperportion of said tubes at mist preventing temperatures, absorbingsubstantial quantities of S03 by means of said H2804 during its downwardow, and withdrawing fuming sulphuric acid of high concentration at thebottom portion of said tubes at a region where the temperature isapproximately the lowest.

9. The method of producing fuming sulphuric acid which comprisesestablishing gradually decreasing cooling temperatures in an elongatedcondensation chamber, introducing H20 and S03 vapors into the topportion of said chamber, said S03 being present in substantial excessover the quantity necessary to form H2S04 with the H20 present,condensing H2S04 at relatively high condensing temperatures in theuppermost portion of said chamber corresponding to the quantity of H20present, conducting the remaining S03 vapors downward co-currently withthe formed H2S04, absorbing substantial quantities of the excess S03 bymeans of said condensed liquid H2S04 trickling downwards at relativelylow cooling temperatures to form fuming sulphuric acid, withdrawingfuming sulphuric acid of high concentration at the bottom of theapparatus, separately withdrawing residual S03 vapors for introducinginto a washing apparatus, absorbing said vapors by means of H2S04 ofabout 95% whereby H2504 of 97% is obtained, diluting part of said acidto a concentration of and returning said diluted acid to the saidwashing apparatus.

10. The method of producing fuming sulphuric acid which comprisesestablishing a downward ilow of S03 and H20 vapors in a verticalcondensation chamber, said S03 being present in substantial excess overthe quantity necessary to form H2S04 with the H20 present, establishingan external upward ilow of a cooling liquid around the outer surface ofsaid chamber in controlled heat exchange with the contents thereof toprovide a mist preventing cooling rate between the dew point of saidvapors and about C. in the upper portion of said chamber andtemperatures gradually decreasing to about 26 C. in the lower portion ofsaid chamber, condensing H2S04 corresponding to the quantity of H20present in the upper portion of said chamber, absorbing relatively largeamounts of S03 vapors by means of the condensed H2S04 tricklingdownwards in the lower portion of said chamber, and withdrawing fumingsulphuric acid having a concentration of about 35% at the bottom portionof said chamber.

11. The method of producing fuming sulphuric acid which comprisesintroducing S03 and H20 vapors at a temperature of about 350 C. into avertical condensation chamber at the top thereof, said S03 being presentin substantial excess over the quantity necessary to form H2804 with theH20 present, establishing an external upward flow of a cooling liquidaround the outer surface of said chamber in controlled heat exchangewith the contents thereof to provide a cooling time of about 0.2 to 0.6second between the dew point of said vapors and about C. in the upperportion of said chamber and temperatures gradually decreasing to about26 C. in the lower portion of said chamber, condensing H2S04corresponding to the quantity of H20 present in the upper portion ofsaid chamber, absorbing relatively large amounts of S03 vapors by meansof the condensed H2SO4 trickling downwards in the lower portion of saidchamber, said withdrawn fuming sulphuric acid having a concentration ofabout 35% at the bottom portion of said chamber.

12. The method of producing fuming sulphuric acid which comprisesestablishing a downward flow of S03 and H20 vapors in a verticalcondensation ,chamber at velocities of flow from about 0.8 to about 5.0metres per second, said S03 being present in substantial excess over thequantity necessary to form I-I2S04 with the H20 present, establishing anexternal upward flow of a cooling liquid around the Outer surface ofsaid chamber in controlled heat exchange with the contents thereof toprovide a cooling time not less than about 0.2 second between the dewpoint of said vapors and about 140 C. in the upper portion of saidchamber and temperatures gradually decreasing to about 26 C'. in thelower portion of said chamber, condensing I-I2SO4 corresponding to thequantity of H20 present in the upper portion of said chamber, absorbingrela,- tively large amounts of S03 vapors by means of the condensedH2S04 trickling downwards in the lower portion of said chamber, andwithdrawing fuming sulphuric acid having a concentration of about 35% atthe bottom portion of said chamber.

13. The method of producing fuming sulphuric acid which comprisesestablishing a downward ilow of S03 and H20 vapors in a verticalcondensation chamber, said S03 being present in substantial excess overthe quantity necessary to form H2S04 with the H20 present, establishingan external upward ow of a cooling liquid around the outer surface ofsaid chamber in controlled heat exchange with the contents thereof toprovide a mist preventing cooling rate between the dew point of saidvapors and about 140 C. in

the upper portion of said chamber and temperatures gradually decreasingto approach that of the cooling medium in the lower portion of saidchamber, condensing H2S04 corresponding to the quantity of H20 presentin the upper portion of said chamber, absorbing relatively large amountsof S03 vapors by means of the condensed H2S04 trickling downwards in thelower portion of said chamber, and withdrawing fuming sulphuric acid atthe bottom portion of said chamber.

14. The method of producing fuming sulphuric acid which comprisesintroducing S03 and H2O vapors at a temperature of about 350 C. into avertical condensation chamber at the top thereof, said S03 being presentin substantial excess over the quantity necessary to form H2S04 with theH20 present, establishing an external upward iiow of a cooling liquidaround the outer surface of said chamber in controlled heat exchangewith the contents'thereof to provide a cooling time of about 0.2 toabout 0.6 second between the dew point of said vapors and about 140 C.in the upper portion of said chamber and temperatures graduallydecreasing to that at which the effluent gases are substantially devoidof S03 in the lower portion of said chamber, condensing H2S04corresponding to the quantity of H20 present in the upper portion ofsaid chamber, absorbing relatively large amounts of S03 vapors by meansof the condensed H2S04 trickling downwards in the upper portion of saidchamber, and withdrawing fuming sulphuric acid at the lower portion ofsaid chamber.

15. The method of producing fuming sulphuric acid which comprisesestablishing a downward flow of S03 and H20 vapors in a verticalcondensation chamber at velocities of flow from about 0.8 to about 5.0metres per second, said S03 being present in substantial excess over thequantity necessary to form H2504 with the H20 present, establishing anexternal upward ow of a cooling liquid around the outer surface of saidchamber in controlled heat exchange with the contents thereof to providea cooling time not less than about 0.2 second between the dew point ofsaid vapors and about 140 C. in the upper portion of said chamber andtemperatures gradually decreasing to that of about the cooling medium inthe lower portion of said chamber, condensing H`2S04 corresponding tothe quantity of H20 present in the upper portion of said chamber,labsorbing relatively large amounts of S03 vapors by means of thecondensed H2S04 trickling downwards in the lower portion of saidchamber, and withdrawing fuming sulphuric acid at the bottom of saidchamber.

CONWAY BARON voN GIRSEWALD. WOLFHART SIECKE. MAX WOHLWILL.

